1. Field of the Invention
The present invention relates to a plug cap for connecting to a spark plug of an internal combustion engine, and more particularly relates to a plug cap configuration which induces less wear of a threaded terminal on the spark plug, and has elements which are resistant to wear.
2. Background Art
Utility Model Laid-Open Publication No. Sho. 63-60288 xe2x80x9cPlug Capxe2x80x9d and Utility Model Laid-Open Publication No. Sho. 63-87277 xe2x80x9cAttaching Structure for Plug Cap with Integrated Ignition Coil of an Internal Combustion Enginexe2x80x9d show conventional plug cap configurations. In FIG. 5 of publication No. 63-60288, a cylindrical member 15 is fixed to a terminal 4a by a pin member 17 meshing with the terminal 4a. A threaded terminal is in FIG. 4. In FIG. 3 of publication No. 63-87277 a plug cap is shown which has an integrated ignition coil IC built into a plug cap C. The plug cap C is therefore heavy and the load is borne by a shroud 4 via a seal bar S.
FIGS. 15(a) to (c) are views describing the operation of a conventional pin member. FIG. 15(a) shows a configuration having a straight section 103 of a spring pin housed in a groove 102 of a cylindrical member 101. Member 101 meshes with a screw thread 105 on the terminal side. FIG. 15(b) is a view showing the operation when beginning extraction of the cylindrical member 101. When the cylindrical member 101 is moved upwards, a force in the direction of arrow A acts on the straight section 103. This force is orthogonal to an inclined surface of the screw thread 105, and when the force changes direction to that of direction of arrow B, a horizontal component of this force is generated in the direction of arrow C. The straight section 103 then pushes out towards the left due to the horizontal component of the force in the direction of arrow C. As a result, as shown in FIG. 15(c), the straight section 103 moves as far as the top of the screw thread 105, and the cylindrical member 101 is withdrawn in the direction of the vertically extending arrow.
FIGS. 16(a) to 16(c) are views showing difficulties arising in the use of conventional plug caps. FIG. 16(a) shows depressions 106 that are generated by the hard straight section 103 wearing upon the relatively soft screw thread 105 during long periods of use. As shown in FIG. 16(b), when it is intended to withdraw the cylindrical member 101 upwards, the straight section 103 cannot be moved horizontally (in the direction X in the drawings) by applying force to the straight section 103 in the direction of arrow A, due to the depth of the wear-induced depressions 106.
FIG. 16(c) is an enlarged view of FIG. 16(b). In this figure it can be seen that when the center of the straight section 103 reaches, for example, a point P2 which is further inward than point P1, the straight section 103 cannot now be pushed horizontally. Conversely, if the center of the straight section 103 is further left of or outward from point P1, lateral movement is still possible. However, after long periods of use, it is possible that the center of the straight section 103 will the point P2 inward the point P1. Regarding this point, in the case of a plug cap integrally fitted with an ignition coil as in Publication No. Sho. 63-87277, in order to fix the plug cap to the terminal in a reliable manner, it is necessary to make the spring force of the pin member large. When the spring force is large, the wear of the screw threads occurs after a relatively short period of time.
In the above, a description is given of wear on the side of the threaded terminal of the spark plug, but the same also occurs on the side of the cylindrical member of the plug cap.
FIGS. 17(a) and 17(b) are views showing examples of deficiencies in conventional cylindrical members. FIG. 17(a) shows that the width of the groove 102 is substantially the same as the diameter of the straight section 103. This straight section 103 moves up and down so as to knock against an upper sidewall 107 and a lower sidewall 108 during vibration. As a result, as shown in FIG. 17(b), the sides of the relatively soft sidewalls 107 and 108 are deformed and a so-called tadpole shape is formed. The straight section 103 meshes as a result of movement to the right in the drawings and is released as a result of movement to the left. Movement to the left is therefore indispensable if the cylindrical member 101 is to be detached.
In FIG. 17(b), as the straight section 103 is inserted into a concave part 109, it is necessary to apply quite a large force in order to cause movement in the direction of the arrow 3. The operability of the configuration of FIG. 17(a) is therefore low and this configuration is not preferred. As shown by these illustrations, conventional configurations are seen to develop a considerable reduction in operability after extended use.
It is therefore an object of the present invention to prevent the occurrence of depressions at the screw threads on the terminal side.
It is further an object of the present invention to prevent the occurrence of depressions in a groove on the side of a cylindrical section.
It is an additional object of the present invention to prevent a reduction in operability in detaching the plug cap.
In order to achieve the aforementioned objects, a plug cap attachment method is disclosed utilizing a plug cap having a conductive section covering the threaded terminal, a groove cut to a fixed depth from the outer surface of a cylindrical section towards the center thereof, and an alignment section of an attachment element installed at the groove. The attachment element may be a spring pin having a substantially straight section serving as the alignment section. The straight portion of the spring pin meshes with the threaded terminal, with the threaded terminal located on a spark plug installed in an internal combustion engine. The spark plug is typically installed in a manner substantially parallel to the cylinder axis of an ignition chamber. When the plug cap is connected to the spark plug, the straight section of the spring pin lies in a plane orthogonal to the axis of a crankshaft of the internal combustion engine.
Vibrations of the internal combustion engine mainly occur in a plane orthogonal to the axis of the crankshaft. Therefore, when the straight section of the spring pin is arranged in this plane, the threaded terminal is arranged in parallel with this surface. External force therefore operates in each direction in this plane but external forces do not generally operate in directions orthogonal to this plane. Because the external force does not operate in a direction orthogonal to this plane, there is no knocking of the screw thread and no danger of depressions being created at the screw thread.
The internal combustion engine can be mounted on a vehicle in such a manner that the crankshaft extends across the width of the vehicle and the cylinders are above the axis of the crankshaft. A main direction of vibration of the internal combustion engine is therefore substantially orthogonal with the cylinder axis and the axis of the crankshaft, and the straight section of the spring pin extends in parallel with the main direction of vibration. Because the straight section is parallel to the direction of vibration, external force does not operate in a direction orthogonal to the pin axis, and there is no danger of knocking at the screw thread or at sidewall grooves. There is accordingly no danger of depressions occurring at the screw thread or groove sidewalls.
The main direction of vibration of the internal combustion engine is typically in a direction from the front to the back of the vehicle, the cylinder axis of this internal combustion engine being substantially vertical and the straight section of the spring pin extending substantially in a direction from the front to the back of the vehicle.
In addition to there being no danger of depressions occurring in the screw threads and the sidewalls of the grooves, it is also anticipated that unpleasant vibrations sensed by a motorcycle rider will be substantially reduced. If a seat is located above an inclined engine in a motorcycle in which the principal vibrations from an engine are vertical, this provides an unpleasant feeling during riding. If the direction of vibration is then made from the front to the rear of the vehicle, the unpleasant vibrations are substantially reduced.
The present invention also involves a plug cap having a conductive cylindrical section into which a threaded terminal of a spark plug is screwed and incorporated at the lower part of a cap body. A groove is cut into the cylindrical section to a fixed depth, with a straight section of the spring pin installed at the groove and meshing with the threaded terminal. An identifying part for identifying the direction of the straight section is formed in the cap body. The occurrence of depressions in threaded terminals can be suppressed by lining up the direction of attachment of the straight section of the spring pin with the direction of the vibrations acting on the spark plug. However, the spring pin and the straight section thereof are within the cap body and their orientation cannot be determined from the exterior of the plug cap. The identifying part is therefore provided as a mark, such as an arrow, a character, a color, an indentation, a raised surface or surfaces, a luminescent element, or other identifying indicia on the cap body, to provide an indication of the proper orientation of the cap body from the exterior.
The cap body may comprise a cylindrical section with a conductive cylindrical section built in the body, and a connector for supplying electricity to the conductive cylindrical section from outside. The connector can include the identification section because the connector extends from the cylindrical section at a right angle to the axis of the cylindrical section.
A method of applying an identifying mark is also disclosed, in which characters or a color are applied to the cap body as an identification part. If the connector itself is used as an identification part indicating direction at the cap body, increases in costs can be kept down while maintaining an attractive appearance. In this case the cap body or an element of the cap body lies in a predetermined alignment with a straight section of a securing spring pin or pins within the plug cap. The element having a predetermined alignment is then used to determine the proper alignment when installing the plug cap in relation to the primary direction of vibration of the engine.
The ignition coil can include a primary coil and a secondary coil which is built into the cap body. The plug cap having an integrated ignition coil is substantially heavier than those having an external transformer. The spring force of a securing spring pin must therefore be increased to reliably fix the cap to a threaded terminal. This increase in spring force results in a striking increase in the occurrence of depressions in the screw thread and depressions in the groove. However, in the present invention, even a plug cap with an integrated ignition coil can be reliably attached to a screw terminal by lining up the direction of vibration applied from outside and the axial direction of the pin of the straight section of the spring pin. In addition, depressions do not occur and detachment from the spring terminal is straightforward.
Further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.